Bidleman, Terry

Abstract [en]

Four different commercially available cyclodextrin (CD) capillary gas chromatography (GC) columns were tested for the enantioselective separation of nine environmentally persistent atropisomeric 3- and 4-methylsulfonyl PCBs (MeSO2-CBs). The selected columns contained cyclodextrins with various cavity diameters (β- or γ-CD), which were methylated and/or tert-butyldimethylsilylated (TBDMS) in the 2,3,6-O-positions. The β-CD column with TBDMS substituents in all of the 2,3,6-O-positions was by far the most selective column for the MeSO2-CBs tested. Enantiomers of congeners with 3-MeSO2 substitution were more easily separated than those with 4-MeSO2 substitution. The separation also seemed to be enhanced for congeners with the chlorine atoms on the non-MeSO2-containing ring and clustered on one side of the same ring. The 2,3-di-O-methyl-6-O-TBDMS-β-CD was found to give somewhat better selectivity than the corresponding γ-CD, in comparison between the two columns, which were identical in all other respects. Enantioselective analysis of arctic ringed seal (Phoca hispida) and polar bear (Ursus maritimus) adipose tissue revealed a strong dominance of certain enantiomers. For example, the enantiomer ratio (ER) of 3-MeSO2-CB149 was 0.32 and <0.1 in ringed seal blubber and polar bear fat, respectively. These low ER values are indicative of highly enantioselective formation, enantioselective metabolism, enantioselective transport across cell membranes, or a combination of the three in both species. Comparable results for the enantiomeric analysis of MeSO2-CBs in biotic tissue extracts were obtained using two highly selective mass spectrometric techniques, ion trap mass spectrometry/mass spectrometry and electron capture negative ion low-resolution mass spectrometry.

Wiberg, Karin

Umeå University, Faculty of Science and Technology, Department of Chemistry.

2002 (English)Doctoral thesis, comprehensive summary (Other academic)

Abstract [en]

Many persistent organic pollutants (POPs) are chiral. These pollutants are generally released into the environment as racemates, but frequently undergo alterations in enantiomeric composition as soon as they are subjected to life chemistry processes. Enantiospecific analysis of chiral POPs is important since enantiomers of chiral compounds often exhibit differences in biological activity, and most biochemical processes in nature are stereospecific. For abiotic processes, such as air-water gas exchange, deposition and long-range air transport, enantiomeric patterns of POPs may be used as chemical markers.

The aim of the work described in this thesis was to improve our knowledge about the presence and fate of enantiomers of chiral POPs inthe environment to provide a sound basis for accurate risk assessment. The compounds included were organochlorine (OC) pesticides (α-HCH, chlordanes and o,p’-DDT), atropisomeric PCBs and some of their respective metabolites (heptachlor-exo-epoxide, oxychlordane and MeSO2-PCBs).

Analytical methods for chiral PCBs were developed, and the elution sequences of (+) and (−)-enantiomers were determined. Enantiomeric fraction (EF) was proposed as a better reflector of chiral composition than the conventional enantiomeric ratio (ER).

Enantioselective bioprocessing in various compartments was studied, with the main emphasis on factors controlling chiral composition in biota Correlations were detected between changes in EFs and differences in trophic levels. The changes were, however, not consistent for all compounds. Instead, the enantiomeric composition was found to be species-specific in the polar bear food chain and in aquatic species from the Baltic Sea. The EFs of some POPs in Baltic seals were related tonutritional status and biotransformation capacity.

Enantiomeric and isomeric patterns were used to investigate abiotic processes in the southern Baltic Sea environment and EFs were used tostudy soil as a source of atmospheric heptachlor-exo-epoxide.